1. Field of the Invention
The present invention relates to a data sequence conversion circuit for converting a plurality of input data sequences having different data widths into output data sequences having a prescribed data width, and also relates to a printer using the same.
2. Description of the Related Art
An LED printer is a form of electrophotographic image forming apparatus, and uses an LED array head as a means for exposing optical image information onto a photosensitive drum. Such an LED array head comprises: an LED array consisting of a row of LEDs arranged at prescribed pitch; a shift register consisting of storage elements each for storing one image data unit corresponding to one LED, the number of storage elements being the same as the number of LEDs; and an LED driving circuit for driving the LEDs to emit light in accordance with the image data stored in the shift register.
With increasing LED printer speed, and with increasing resolution and printing width, the amount of image data, that is transferred into the register section of the LED array head within a unit time, has increased. To increase the speed of image data transfer to the register section without increasing the transfer clock frequency of the shift register, the LED array head employs a parallel shift register configuration in which a sequence of image data corresponding to the plurality of LEDs is input simultaneously in parallel form.
The printing resolution of an LED printer is determined by the pitch of the LED arrangement. Japanese Unexamined Patent Publication No. 7-156442 discloses an LED printer that uses an LED array consisting of LEDs arranged at a pitch corresponding to the pixel pitch of resolution equal to the least common multiple of a plurality of different resolutions. For example, image data of resolutions 240 dpi, 300 dpi, and 400 dpi are printed using an LED array head having a resolution of 1200 dpi which is the least common multiple of the image data resolutions.
The above Unexamined Patent Publication number also discloses an LED printer in which, using the fact that one pixel unit of low resolution print data is formed by a plurality of LEDS, control is performed to add smaller print dots around an attention pixel or erase smaller print dots from an attention pixel by individually and selectively lighting or extinguishing the LEDs forming the pixel unit. That is, the LED printer disclosed therein has the function of correcting for jagged edges (jaggies) that appear when printing a low resolution image.
In an LED printer that prints low resolution print data of 240 dpi, 300 dpi, and 400 dpi using an LED array head having a resolution of 1200 dpi which is the least common multiple of the print data resolutions, one dot of print image data of 240 dpi is formed from five print dots of 1200 dpi, one dot of print image data of 300 dpi is formed from four print dots of 1200 dpi, and one dot of print image data of 400 dpi is formed from three print dots of 1200 dpi. When the jaggy correction method described above is applied to this LED printer, a jaggy correction circuit determines a pattern of five, four, or three high resolution print dots, respectively, and outputs the pattern at the attention dot position of the low resolution print data of 240 dpi, 300 dpi, or 400 dpi, respectively. That is, one unit of data output from the jaggy correction circuit varies depending on the resolution of the input low resolution print image data.
If an LED array head employing a parallel shift register configuration is used as the LED array head of 1200 dpi, the data width of the parallel input to the LED array head does not necessarily coincide with the width of the print dot pattern that the jaggy correction circuit outputs. Data sequence conversion is therefore needed for converting the output data sequence of the jaggy correction circuit, which varies depending on the input image data resolution, into a data sequence that matches the data width of the parallel input to the LED array head.
A data sequence conversion circuit may be constructed using a PS conversion circuit, which applies a parallel-to-serial conversion to the output data of the jaggy correction circuit, and an SP conversion circuit, which applies a serial-to-parallel conversion to the PS converted output so as to match the parallel input data width of the LED array head, and the data sequence conversion may be accomplished by applying a suitable control signal (clock signal).
However, in the data sequence conversion circuit of the above configuration, since the print dot data is first converted into serial data, this is equivalent to serially transferring the high resolution print dot data. Accordingly, the data conversion circuit must be constructed using high speed operating shift registers, defeating the purpose of the LED array head of the parallel shift register configuration in which the print dot data are input in parallel in order to increase the print speed without increasing the frequency of the shift register transfer clock.